We propose to investigate the cellular organization of the mammalian lens and its possible relation to cataract by determining the three-dimensional structure of the fiber gap junctions. Up to 60% of the lens fiber surface is composed of junctions that are thought to belong to the communicating type. This unique cellular arrangement will allow the study of cell communication at the molecular level. We will investigate the junctions in isolation by electron microscopy and X-ray diffraction methods to determine three basic characteristics of the functional units (connexons): a) the oligomeric arrangement of the connexons, b) the secondary structure of the connexon subunit; and c) the conformational changes that the connexons must undergo to mediate and regulate permeability. In addition, by reconstituting the connexons into unilamellar liposomes, we shall measure the permeability changes in vitro to test directly the hypothesis that connexons are the units mediating and regulating permeability.